FIG. 8 shows the outlook of a van-type vehicle having a slide seat which is used by the physically handicapped person when the physically handicapped person gets on and off the vehicle. A slide door SD at a side surface of the vehicle is opened so that a seat ST for the vehicle is advanced to a lower position, near a road surface, outside the vehicle by a slide device SE. As shown in FIG. 9, the slide device SE is constructed of a pair of parallel outer rails 101 disposed outermost, a pair of parallel middle rails 102 disposed inward from the outer rails 101, and a pair of parallel inner rails 103 disposed inward from the middle rails 102. The left and right middle rails 102 and the left and right inner rails 103 are integrated with each other with cross members 104, 105 installed at front and rear positions of the slide device SE.
The seat ST (FIG. 8) is placed on the inner rails 103 through a seat bracket (not shown). The outer rail 101 is placed on a rotary disk installed in an inclined posture on a slide mechanism (not shown) disposed in the longitudinal direction of the vehicle by means of a bracket 106. When the physically handicapped person gets on and off the vehicle, the entire slide device SE is directed orthogonally to the longitudinal direction of the vehicle by means of the rotary disk, and the middle rail 102 and the inner rail 103 are slid in an advance direction by means of a ball thread driving mechanism, as shown in FIG. 10 to locate the seat ST placed on the inner rail 103 near the road surface. Because the slide device SE can be advanced in a two-stage system, except when the physically handicapped person gets on and off the vehicle, the slide device SE is accommodated compactly inside the space-limited vehicle by moving the rails 102, 103 rearward.
As the construction for sliding the middle rail 102 relative to the outer rail 101 and the inner rail 103 relative to the middle rail 102, as shown in FIG. 11, a guide groove 107 triangular in section extending in the longitudinal direction of the rails is formed on a confronting surface of the rails 101 through 103, and a plurality of balls 85 held by ball guides (not shown) respectively is disposed at predetermined intervals in the space between the guide grooves 107. The slide device is disclosed in Japanese Patent Application Laid-Open No. 2001-130293.
However, in the above-described conventional slide device, when the seat is advanced outward from the vehicle, by the weight of a person and the dead weight of each rail, a high offset load is applied in such a way as to vertically shift the rear-end portion of the inner rail 103 and the rear-end portion of the middle rail 102 relative to the front-end portion of the middle rail 102 and the front-end portion of the outer rail 101 respectively. Such being the case, heretofore, to prevent the groove surface of the guide groove 107 from being damaged by the above-described offset load, the guide groove 107 is quenched. But the quenching has a problem that much time and labor are required in a quenching operation and in correcting the groove surface which is deformed by the quenching. Further it is necessary to perform processing of forming holes such as installing holes for installing the cross members 104, 105 and processing of cutting the guide groove 107. In addition, it is necessary to perform a work of installing the cross members while making accurate adjustment of parallelism between the left and right rails 101 through 103.
The present invention is intended to solve the above-described problems. Therefore it is an object of the present invention to provide a slide device which can be manufactured and assembled easily.